1. Field of the Invention
The present invention relates generally to wireless communication systems, and more particularly to using switched, distributed antennas in a wireless communication system.
2. Related Art
Typically, a wireless communication system (such as a cellular telephone system) covers a relatively large geographical area. The mobile units (also called, simply, mobiles) in this typical wireless communication system are usually positioned outside of buildings and communicate with base stations located on towers that are distributed throughout the coverage region. Accordingly, this typical system is called herein an "outdoor" wireless communication system.
It is desirable to establish a wireless communication system within a building (i.e., an "indoor" wireless communication system). This indoor wireless system would preferably support mobiles located throughout the interior of the building that communicate with base stations located within the building.
Indoor wireless systems, however, face many technical challenges. For example, mobiles can be distributed throughout an area that is much larger than the coverage achievable with a base station having a single antenna that is radiating an officially sanctioned, transmitted power level. The use of multiple, complex base stations to improve coverage is expensive.
In addition, an indoor RF (radio frequency) propagation path is characterized by multipath fading effects that result in the production of multiple copies of the desired signal being created by reflections and scattering off of objects located in the propagation path. These multipath signals vary in amplitude and phase with respect to each other, such that at the receiver, the vector sum of all of these signals cause the envelope of the resultant RF carrier to undergo rapid fluctuations in amplitude and phase as a function of position, time and frequency.
Also, pulsed or digital signals (which are typically used in wireless communication systems), which are composed of many frequency components having precise phase and amplitude relationships to one another, are very prone to distortion due to time and frequency dispersion (i.e., the propagation time and path attenuation vary with frequency). In addition, path attenuation varies over a wide range of power laws in both distance and direction because of the complex nature of such scattering and absorption. The arrival of a pulse of energy will be spread in time due to the reception of multiple "copies" of the pulse that have been reflected off both stationary and mobile scatterers. The individual replicas of the pulse arrive at the receiver at different times because of the different path lengths. This time delay spread of digital signals causes intersymbol interference (ISI), limiting the signaling rate for a desired level of error rate performance.
Thus, what is required is an indoor wireless communication system which efficiently and effectively addresses the above technical challenges.